Electrophotographic liquid developing process employing non-polymer binding materials in the photoconductive

ABSTRACT

This invention relates to an electrophotographic photosensitive member and process of electrophotography. The member comprising a base and a photoconductive layer formed on the base, the photoconductive layer containing photoconductive substances and nonpolymers as bonding materials. The image forming process comprising the steps of forming an electric latent image on the photoconductive layer, developing this formed latent image with a developer for wet-sticking the developer to the latent image region.

United States Patent Inoue et al.

[Ill 3,876,424

ELECTROPHOTOGRAPHIC LIQUID DEVELOPING PROCESS EMPLOYING NON-POLYMER BINDING MATERIALS IN THE PHOTOCONDUCTIVE Inventors: Eiichi Inoue; lchiro Endo, both of Tokyo, Japan Assignee: Canon Camera Kabushiki Kaisha,

Tokyo. Japan Filed: June 19, I972 Appl. No.: 264,335

Related US. Application Data Continuation of Scr. No. 800,529. Feb. 19, I969, abandoned.

Foreign Application Priority Data Feb. 26, I968 Japan 43-] I800 Feb. 26, I968 Japan 43-1 I801 Feb. 26. 1968 Japan 4 I 43-] I802 Mar. 5. 1968 Japan 43-14230 Apr. 30. I968 Japan 43-29256 May 9, I968 Japan I. 43-381 I2[U] May 30. 1968 Japan 43-37l93 U.S. Cl. 96/] LY; 96/l.5; 96/l.8;

I l7/37 LE Int. Cl. G03g 13/10; (103g 5/04 Field of Search 96/1 LY, L5. L8;

I l7/37 LE 1 Apr. 8, 1975 [56] References Cited UNITED STATES PATENTS 3.245.38l 4/1966 Brenneisen et al 96/1 LY 3.285.74l Il/l966 Gesierich et aI 96/] R 3.383.209 5/1968 Cassiers et al. 96/I R X 3.396016 8/1968 Olson.l 96/I.8 3.406.063 lO/l968 Matkan et aI 96/].8 X 3.425.829 2/l969 Cassiers et al. ll7/37 LE 3.460.476 8/l969 Swigert et al. 96/l.5 X 3,547,627 I2/I970 Amidon et al. 96/l.5 X 3.607.261 9/I97l Amidon et al. 96/l.5 X 3,676.2l5 7/I972 Gundlach ll7/37 LE X 3,698.3l2 l0l|972 Miiller 96/] LY X Primary E.\'aminer-Norman G. Torchin Assistant ExaminerJohn R. Miller Attorney, Agent, or Firm-Fitzpatrick, Cella. Harper & Scinto [57] ABSTRACT gion.

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.nhhlmlw weunglg i ig ELECTROPHOTOGRAPHIC LIQUID DEVELOPING PROCESS EMPLOYING NON-POLYMER BINDING MATERIALS IN THE PHOTOCONDUCTIVE This is a continuation, of application Ser. No. 800,529, filed Feb. I), I969 now abandoned.

This invention relates to an electrophotographic pho tosensitive member and more particularly to an electrophotographic photosensitive member used in wet developing method and to a novel process thereof.

Numerous types of electrophotographic methods used for copying documents etc. have already been proposed, however. in all of these methods. an original picture is recorded in photosensitive member as an electrostatic image by projecting the optical image of the original picture onto the photoconductive layer provided in the photosensitive member, by such means as selectively eliminating the electric charges on the photoconductiw layer. that has previously been charged uniformly, corresponding to the optical image or inducing electrostatic charges corresponding the optical image projected. and by forming an electrostatic pattern consisting of the pattern of electrostatic charges that correspond to the optical image in the photoconductive layer or in other layers. Various methods have already been proposed to form a visual image by developing the electrostatic latent image formed as mentioned so far. A known method is to apply a colored toner charged either in the same polarity as or in a different polarity from the electrostatic latent image to the photosensitive member holding the electrostatic latent image, and to develop the image by having the electrostatic latent image attract the said toner electrostatically. ln this method, dry type developing agents, in which the toner is adhered electrostatically to a holding body called the carrier. are in general use. But liquid type developing agents that contain the toner are also known to the public.

One of the known types of liquid developing agents is to use the developing agents in the form of aerosol. With this type of developing agent, development is con ducted by charging the atomized toner ofa dye solution electrostatically in high pressure equipment, by spraying the toner in an electric field between two electrodes one of which is the photosensitive member holding the electrostatic latent image, and by adhering electrostatically the charged atomized toner onto the electrostatic latent image. The second type of developing agent is one in which the toner is dispersed into and suspended by holding liquids having a high electrical resistance and a low dielectric constant such as benzene, benzol, and carbon tetrachloride and simultaneously charged in a polarity different from that of the electrostatic latent image of photosensitive member. The photosensitive member is immersed into the developer and the development is carried out by attracting and adhering the aforementioned toner onto the electrostatic latent image of the photosensitive member.

However. these known electrophotographic methods which employ liquid type developing agents have grave defects. In the first type of method. equipment is needed to generate high voltage electricity. This results not only in extremely high cost but also is extremely dangerous to the human body and requires complete care in handling the equipment. In the second type of method, almost all the holding liquids that suspend the toner in developing agents are combustible and are physiologically disgusting and hazardous to the human body. This requires that special attention be given to the handling of developer in order to avoid such disturbances. Moreover, since the holding liquids are generally organic solvents, the photosensitive members that use such type of developer are limited to be those that are made of materials that withstand the said organic solvents.

In order to remove these defects, the socalled wetting developing method, which, quite different from the aforementioned methods, develops the electrostatic la tent image by having the electrostatic force ofthe electrostatic latent image on the photosensitive member exert influence on the interfacial tension between the developer and the surface of the photosensitive memher when the developer is applied to the photosensitive member and by having the developer stick to the photosensitive member selectively, gas disclosed in U.S. Pat. Nov 3,084,043. Although the so-called wetting developing system uses a liquid type developing agent like the aforementioned electrophotographic methods, the developing mechanism is quite different from those of the aforementioned methods. The principle is based on the fact that when a liquid is applied to the surface of a body by the electrostatic force the interfacial tension of the surface of the body changes at the interface between the liquid and the surface of the body and the surface of the body exhibits wetting action. Explained in more detail, the action by which a liquid wets the surface of a specific body can be expressed by the socalled contact angle. The term contact angle is defined as the angle between the surface of a body and the tangent line to the surface of a liquid drop resting on the surface. Generally, when the surface of a body is wet ted by a liquid, the contact angle assumes an angle of or less, and when not wetted. more than 90. How ever, it is a known fact that, when a liquid applied to the surface of an body having a contact angle of over 90, and when electrostatic charge is present on the surface of said body, the contact angle is reduced to 90 or less by the electrostatic force of the charge. In other words, the surface ofa body produces wetting action by electrostatic force. Consequently, when an electrostatic image is formed on the photosensitive member. the portion where the latent image is present attracts the developer because of the wetting action and the remaining portion scarcely attracts the developer because ofthe poor wetting action, and, as a result development is carried out. The wetting action of the surface of the photosensitive member is performed either selectively or in different degrees and. in correspondence with it, the developer adheres to the photosensithe member either selectively or in different degrees, and, as a result, development is completed. In particular, the developers used in the wetting developing system differ remarkably in composition from the developers used in the aforementioned well known electrophotographic methods. The toner suspensions used in the aforemen tioned electronic photographic methods usually use organic solvents, whereas the developers employed in the wetting developing system use a solution of aqueous system having a high dielectric constant such as water instead of organic solvents. Therefore, in contrast to organic solvents, the developers ofthe wetting develop ing system are not combustible, cause no disturbance on human body and in these respects are very effective in practical use.

However. as to the photosensitive member used in the wetting developing system. polymers have been used as the film forming substances. This caused nonuniformity in the properties of the photosensitive member and it was impossible to obtain photosensitive members of constant characteristics. The conventional known photosensitive members are formed. for example. by dispersing pulverized photoconductive body such as zinc oxide into film forming polymers such as silicon resins. styrene resins. and butadiene resins. by applying a coat of the suspensions to a paper or metal base. and by drying. However. since in such photosensitive members high molecular polymers present on the surface of photoconductive material such as zinc oxide is being adsorbed. polymers of different compositions appear and are distributed on the surface that receives the developer and. as a result. the photosensitive members so obtained had a surface on which the lyophilic and lyophobic sections are nonuniformly dispersed. Consequently. even when uniform electrostatic charge is present on the photosensitive member. uniform sticking of developer is impossible because of the effect of aforementioned nonuniformity of lyophobic and lyophilic sections. and even when an electrostatic latent image is formed on the photosensitive plate. only an extremely fogged and bad picture image was obtained by wetting development. Moreover. since the aforemen tioned photosensitive members employ polymers as film forming materials. the photosensitive members obtained were forced to be very thick.

Furthermore. conventional photosensitive members offered for use in wetting development employ such conductive substances as foils of aluminum. copper or zinc or glass and paper as the base for photoconductive layer. An electron photographic process. in which a visual image is formed by projecting an optical image onto a photosensitive member of such composition. by applying an voltage of some hundreds of volts to the said photosensitive member either successively or si multaneously. by making the developing roller hold the developer in contact with the surface ofthc photosensitive member and to rotate the developing roller and by sticking the developer to the portion of the optical image projected section that shows wetting action. was also known to be public. However. in electronic photographic methods employing such wetting developing methods as have so far been offered. the lyophilic and lyophobic sections are nonuniformly distributed on the surface of the photosensitive member as mentioned above. and one was unable to obtain a constantly favorable picture image.

Furthermore. the photoelectric layer used in the aforementioned well known example had a comparatively high dark resistance of about cm and, at the same time. used conductive materials as the base as mentioned above, had the following disadvantages in forming latent image:

When an optical image is projected onto the photosensitive member having the aforementioned composition. free carriers are generated in the photoconductive layer that corresponds to the light portion of the optical image. and many carriers move to the neighborhood of the surface of the photoconductive layer to form an electrostatic latent image. However. since the specific resistance of the photoconductive layer is comparatively high. the speed of the movement of carriers is not high, as a result. only low speed photosensitive members were obtainedv Furthermore. since the base was formed with conductive materials. when the developing roller rolls on the photosensitive member after the projection of the optical image. electric charges opposite in polarity to the aforementioned carriers are injected from the said roller into the photosensitive layer. These electric charges are recombined with the charges forming the aforementioned electrostatic latent image. and reduce the effective charges of the latent image, and destroy the electrostatic latent image that has already been formed. As for the developer supplying means such as the developing roller used to supply a developer employed in the conventional wetting developing systcm to the surface of the photosensitive member, the one that has a geometrically uneven surface and has the developer filled in the said depressions was disclosed by the US. Pat. No. 3.084.043. The one which has a rollershaped surface having grooves 0.01 l mm deep on the surface of the roller which are filled with developer. and while rotating the roller on the surface of the photosensitive member wet-sticking the developer in the grooves to the portion of the photosensitive member where the electrostatic image is present, was disclosed in Japan Patent Publication SHO 40-18993.

As have mentioned so far, all the developer supplying means that have been disclosed are of the type that has a geometrically uneven surface. depressions of which serve to hold the developer. The reason is that. if the surface ofthe supplying means is plane and smooth. the surface of the photosensitive member is uniformly wet when developing and the developer sticks to the surface equally. Although the developer wet sticks to the surface of the photosensitive member according to the electrostatic latent image or conductive pattern formed on the photosensitive member, the developer is forced to stick evenly to the no-picture area where no such latent image or pattern exists. As a result, the image visualized by the developer has a dense fog.

In order to remove such a defect, several methods have been offered. as were shown in the aforementioned patents. in which the surface of the developer supplying means is formed geometrically uneven. the projections are so designed to be free from the sticking of developer. and only the portion of the photosensitive member where the electrostatic latent image is present is wetted by and attracts the developer being held in the depressions. This prevented the developer from sticking equally to the photosensitive member, and enabled a visual image having an extremely small amount of fog to be obtained. However. since the resolving power of a development by the developer supplying means of such a construction depends upon the fineness of the geometrical unevenness. desired degree of resolving power could not be obtained without making the uneven portion very fine. However. since there was a limit in forming fine unevenness on the surface of developer supplying means. the amount of developer filled in the depressions became smaller as the unevenness became finer. As a result. the amount of liquid supplied to the photosensitive member was reduced and the density of the picture image was caused to be reduced.

Furthermore. the aforementioned developer supplying means have been formed in the shape of a roller. It was a difficult for such roller-shaped means to supply a constant amount of developer continuously. General practice was to feed the ink with a great number of rollers. to supply the ink to an ink feed roller. and to re move the excessive ink finally with a doctor knife. as is usual in the known technique of printing. However. since such a device was complicated and expensive. it was unsuitable for application to common copying devices.

An object of this invention is to offer an elcctrophotograhic photosensitive member for use in wetting development wherein the foregoing defects are removed and each ofthe lyophobic and lyophilic portions is evenly distributed on the surface.

Another object of this invention is to offer an electro photographic photosensitive member for wetting development wherein the surface is capable of adjusting both the lyophobic property and lyophilic property as desired.

A further object of this invention is to offer an electrophotographic photosensith e member for wetting development having a mechanical strength similar to the case in which the conventional film forming polymers are used and is enabled to be composed in very thin layers.

A still further object of the invention is to offer a novel visual-image-forming process wherein a visual image with an extremely high picture density is formed by using a photoconductive layer with comparatively low specific resistance and a base with a highly resistant layer or a barrier layer.

A still further object of this invention is to offer a image forming process. wherein an very clear visual image is obtained by using two kinds of developer for wetting development. one is hydrophobic and the other hydrophilic.

A still further object of this invention is to offer an image forming process. wherein the electric latent image formed on the photosensitive member is reversed and visualized by converting the polarity of the electrode that applies electricity to the developing roller for wetting development.

A still further object of this invention is to offer an image forming process in which visual image with an extremely high density is formed by the use of nonpolymcrs in forming film on the photosensitive member.

A still further object of this invention is to offer a novel wetting development process. wherein the electrostatic latent image on the photosensitive member is visualized by dropping wetting developer in cascade on the said latent image side of the photosensitive member.

A still further object of this invention is to offer a developing process. wherein wetting developer supplying means is employed to form a visual image with less fog, high resolution power. and further an extremely high picture image density.

A still further object of this invention is to offer a developing process, wherein a feed roller supplies the developer uniformly onto the developer supplying means which applies the developer onto the photosensitive member.

Above mentioned and other objects and various ad vantages of this invention will be better understood from the following detailed description taken in connection with the accmpanying drawings in which:

FIG. 1 and FIG. 2 are the drawings showing the principle of wetting development process where a photosensitive member according to this invention is employed;

FIG. 3 is a drawing showing the principle of the lst clectrophotographic image forming process and visual image forming process according to this invention:

FIG. 4 is a sketch of an embodiment of the principle shown in FIG. 3:

FIG. 5 is a drawing showing the principle of the second clectrophotographic image forming and visual image forming processing according to this imention:

FIG. 6 is a sketch of an embodiment of the principle shown in FIG. 5'.

FIG. 7 is a magnified drawing of the feed surface of developer supplying means of first type used in the de velopment processing according to this invention;

FIG. 8 is a drawing showing the principle on which the development of photosensitive member by means of the supplying means shown in FIG. 7 is based;

FIG. 9 shows a front view of the supplying means of FIG. 7;

FIG. 10 is a sketch of a device realizing a develop ment process by using the supplying means shown in FIG. 7;

FIG. II is a magnified cross section of the surface of developer supplying means used in the second type development process according to this invention:

FIG. 12 is a magnified drawing of the surface of the supplying means shown in FIG. ll;

FIG. I3 and FIG. 14 are the sketches of the device which realizes a development process using the developer supplying means shown in FIG. 11 and FIG. [2;

FIG. 15 is a cross section of the device which realizes briefly the dc\elopmcnt process using the wetting developer supplying means according to this invention shown in FIG. 16 through FIG. 21;

FIG. 16 through FIG. 21 show the developer supplying means used in the third type of wetting development process according to this invention;

FIGS. 22 and 23 show other embodiments of the developing device using the feed roller according to this invention;

FIG. 24 is a drawing showing the principle of developing method according to this invention;

A feature of this invention is to provide a photosensitive member for wetting development by using filmforming nonpolymer organic compounds as the bonding materials of photoconductive substances.

Although the wetting developing system is based on the principle that the interfacial tension between a photosensitive member and developer that is applied to the surface of the said member is changed by the effect of the electrostatic latent image formed on the photosensitive member and. as a result. wetting action is produced. and the developer sticks only to the surface of the latent image. it is extremely important in such a wetting developing system to form the surface of the photosensitive member to have lyophobic and lyophilic characteristics in a specified ratio and uniformly as well as to control the relationship between the Iyophobic character and lyophilic character on the surface of the photosensitive member.

Moreover. it is very difficult in wetting developing system to supply constantly the minimum amount of liquid for development to the surface of the photose nsitive member. When an unnecessary amount of developer sticks, fogging is caused to occur, fixing property is degraded. and the only picture images obtained are too poor to be used for practical purposes.

The present inventors found out that these important requirements were fulfilled by controlling the ratio be tween the lyophobic property and the lyophilic property on the surface of the photosensitive member. and also found out that the best way to control the relationship between the lyophobic property and lyophilic property of the photosensitive member was to use nonpolymer organic compounds as the bonding material of film forming photoconductive material.

Generally. nonpolymer compounds have a lyophobic property. The lyophobic property can be controlled arbitrarily by adding further a proper amount of nonpolymers such as. for example. higher fatty acids. higher fatty acid esters. and higher alcohols. The reason for this may be attributable to the fact that. for example. in the case in which zinc oxide is used as the photoconducti\e material and a higher fatty acid is further added. the carboxyl radical of the higher fatty acid is adsorbed chemically to the surface of zinc oxide and the alkyl radical of the higher fatty acid is oriented on the external side of the surface of zinc oxide.

If it is assumed that a highmolecular substance having a large molecular weight or a polymer material is adsorbed or present on the surface of zinc oxide instead of the above nonpolymers, the adsorption and orientation of higher fatty acids on the zinc oxide surface may be disturbed substantially.

On the other hand. in the casein which nonpolymcrs having small molecular weights are used as the bonding materials. the adsorption and orientation of higher fatty acids on the surface of zinc oxide is thought to be disturbed in extremely small degree.

Therefore. when a nonpolymer is used as the bonding material. the lyophobic property of the surface of photosensitive member can be controlled arbitrarily by the addition of a higher fatty acid. Moreover. a nonpolymer is. different from high molecular substances, the polymers. and has a definite chemical composition and, since its molecular weight is small. nonuniformity in electrical characteristic is greatly reduced as the photosensitive member. At the same time. since it is allowed to be dispersed homogeneously. it is possible to distribute the lyophobic property and lyophilic property uniformly on the surface of photosensitive member at a specified ratio.

It is generally possible to control the lyophobic property of the surface of photosensitive member arbitrarily by selecting an appropriate compounding ratio between the photoconductive substance and nonpolymer organic compound.

One other advantage brought about by the use of nonpolymers as the film forming bonding material of photosensitive member is that a very thin layer can be obtained without loosing any electrophotographic characteristicv In other words. a nonuniform thin layer of resin is not formed on the surface any more. and the bonding characteristic with the base or the bonding characteristic in between individual photoconductive substances has a mechanical strength comparable to the case in which conventional film forming polymers are used.

The composition of photosensitive member according to this invention will be described as follow.

The photoconductive materials used in this invention are. for example, zinc oxide. titanium dioxide, zinc sulfide. cadmium sulfide. selenated zinc. lead monoxide. indium oxide. anthracene. anthraquinone. carbazole. and heterocyclic compounds such as imidazole, oxazole. and thiazole.

One example of manufacturing process of electrophotographic photosensitive materials used in this invention is as follows: Prepare a solution of nonpolymer organic compound; Add to it an equal amount or more of photoconductive material and disperse the material by means of an appropriate means such as ultrasonic wave, ball mill. or colloidal mill. Next. apply a coat of the suspensoid on the base such as paper or metal sheet and. dry it to evaporate and remove the solvent. Thus an electrophotographic photosensitive material has been obtained.

The desirable ratio between the amount of nonpolymer organic compounds and the amount of photoconductive materials used in this invention is from 1 to 8 parts by weight of photoconductive materials to 1 part by weight of nonpolymer organic substances. ln this in vention addition of well known sensitizing dyes and chemical sensitizers is possible. if desired. and the sensitizing effect in such cases is quite equal to that of the case in which conventional film forming polymers are used as the bonding agents.

Nonpolymer organic compounds used in this invention are:

A. Organic acids and acid anhydrides: Maleic acid. phthalic acid. salicyclic acid, L-ascorbic acid. abi ctic acid. benzoic acid. naphthenic acid. itaconic acid, adipic acid. sulfosuccinic acid. 2-furan carboxylic acid, alizarine. sebacic acid. lauric acid. myristic acid, terephthalic acid. maleic anhydride. phthalic anhydride. salicylic anhydride.

B. Amine derivatives: Acetophenetidinc. paraminoazobenzen.

C. Phenol derivatives: Phenolphthalein, phenyl salicylate. P-phenylphenol. O-phenylphcnol D. Esters: B-naphthyl methyl ether. dimethyl terephthalate.

E. Aniline derivatives: Diphenyl guanidine. P-benzyl aniline. 2.4,5-trichloroaniline.

F. Amino acids: Aspartic acid. gultamic acid. DL-

valine, alanine.

G. Metallic soap: Zinc naphthate. lead naphthate. co-

balt naphthate, copper oleate. zinc stearate.

E. Sugars and their derivatives: Glucose, sucrose.

1. Phosphorous compounds: Tributyl phosphate, zinc dithiophosphate. zinc pyrophosphate.

.l. Ammonium salts of nonpolymers: Ammonium benzoate, ammonium palmitate, ammonium phthalate, ammonium stealate, ammonium tartrate.

K. Alkali metallic salts of nonpolymer organic compounds: Sodium palmitate, potassium palmitate, potassium picrate, potassium phthalate, apotassium tartrate.

L. Water soluble nonpolymer organic compounds having one or more than one carboxyl radicals. sulfo radicals. phenolic hydroxyl radicals. amino radicals. or halogen radicals: Crotonic acid, maleic acid, benzenesulfonic acid, isocrotonic acid, ethylmaleic acid, dihydroxynaphthenic acid, dinitroph thaleic acid. furan carboxylic acid, P- aminodimethylaniline. hexamethylenediamine. aamino-l-naphthol. acid amides of glycol, 2,5

9 dimethylphenol, P-nitrophenol. dichlorphthalic acid, 2-4-dibrombenzoic acid.

The number of kinds of nonpolymer organic compounds used in the preparation of electrophotographic photosensitive material according to this invention is not limited to one but to two or more than two kinds of the compounds at once. Combined use of high mo lecular bonding materials of high molecular organic photoconductive materials is also allowed when required. Of course, this invention shall not be limited to the compounds described in the specification and examples.

The effective additives that make the surface of electrophotosensitive materials lyophobic in this invention are for example: higher fatty acids such as palmitic acid, stearic acid, behenic acid, oleic acid, and linolic acid; higher fatty acid esters such as linseed oil. perilla oil, olive oil, arachid oil, tsubaki oil, and tung oil: higher alcohols such as stearyl alcohol, myricyl alcohol, and cetyl alcohol.

Sensitizing effect is noticeable by the addition of an appropriate amount of conventional sensitizers to the photosensitive layer used in this invention. The sensitiz ers used are for example: (a) conventional dyes such as Rose Bengal, Phloxine, Erythrasine, Uranine. Eosine, Rhodamine B, Fuchsine, Crystal Violet, Acridine Orange, and Methylene Blue; (b) conventional donor or acceptor additives for photoconductive substances such as maleic anhydride, phthalic anhydride, crotonic acid, benzophenone, hydroquinon, anthraquinone, benzaldehyde, diphenylamine, chloranil, paraphenylenediamine, and aminobenzaldehyde.

The photosensitive member according to this invention will be better understood from the examples I through l described afterwards.

A more specific object of this invention is to offer a novel image forming process by using the photosensitive member comprising the aforementioned materials. This is explained in detail in the following.

All the image forming processes according to this invention have a first feature: the photosensitive member used in the process of this invention has a comparatively low resistant photoconductive layer formed in film on the base with photoconductive materials by using nonpolymers as the bonding materials and the base must have substantially a high resistance. The substantially high resistant base can be referred to an insulating thin film of, for example, Mylar (Trade name of polyester resin) or to the one in which an electrical bar rier layer is formed between the base and photoconductive layer by interposing an epoxy resin layer between these layers. A value of I0 9 cm or more is desirable for the value of high resistance. While the resistance of the photoconductive layer used here is desired to be less than 10 lO Q -cm.

It is generally believed that the resistance of the photoconductive layer of photosensitive member used in electrophotography is required to be [0 -cm or more. This requirement must be fulfilled in in order to form and keep an electrical image on the photoconductive layer and when the resistance is lower than this value a good corona charging characteristic cannot be obtained, that is, such defects as no charging, small amount of charge, or a small charge holding capacity, etc. may be caused and, as a result, it becomes difficult to form a good quality latent image. However, if the specific resistance of photoconductive layer is high, the

photosensitive member has in general a defect of being low in sensitivity.

In this invention, a photosensitive member comprising the aforementioned low resistance photoconductive layer and high resistance base is used to attain the purpose of obtaining a photosensitive member that meets the requirement of electrophotographic photosensitive member and has a high sensitivity. An image forming process using such a photosensitive member will be described in the following.

In this process, an electrostatic latent image is formed by first giving the surface of the aforementioned photosensitive member an exposure oflight and dark pattern in dark place to form a conductive pattern within the photoconductive layer ofthe photosensitive member, then by applying to aforementioned photosensitive member an electric field under condition that an electrode is in close contact with the aforementioned plptosensitive member to form a high electric field at the light portion where the conductivity has been increased by the light and a low electric field at low conductive dark portion.

Next, developer is applied to the surface holding the said electrostatic latent image. The developer wet sticks to the portion where the electrostatic latent image is present, i.e. the light region, and does not stick to the portion where the said latent image is not present. In other words, the developer is selectively attracted by the influence of the electrostatic latent image and, as a result, the electrostatic latent image is visualized.

It is also possible to obtain a reversal image by first forming a colorless pattern due to wet sticking of lyophobic liquid on the electrostatic latent image portion. i.e. the light region, of the photosensitive member by using a colorless lyophobic liquid, and then by applying colored lyophilic second developer to attach the colored developer to the dark region using the repelling power of the lyophobic solution sticking to the photosensitive member.

This invention will be described more concretely by referring to FIG. 3 and FIG. 4.

Taking as an example a photosensitive member comprising a photosensitive layer 1 of ZnO bonding agent system having a rather low dark resistance compared with conventional ones and a base having a resistance almost equal to insulation then, since ZnO is a N- type semiconductor,, the mobility of electrons is greater than the positive holes. that is. it is a majority carrier. Therefore, as shown in FIG. 3a, it is assumed that thermally excited free electron F and the electron T caught at the trap are present in the photosensitive layer even in the dark place. When the surface of the aforementioned photosensitive member is exposed to light and dark pattern, a great amount of free carriers P (positive hole, electron) are thought to be generated in the neighborhood of the surface of photosensitive layer of light portion L (FIG. 3b). Next, when a DC voltage is applied across two electrodes after close contacting the electrode 13 to the photosensitive layer side of the aforementioned photosensitive member and the electrode 13' to the base side, respectively, as shown in FIG. 4, a great amount of negative charge from the light portion L of the aforementioned photosensitive layer, and the remaining negative charge from the dark portion D, are ejected to the electrode (FIG. 3C), and an amount of positive charge equivalent to the amount of charge ejected is considered to be remaining on the photosensitive layer as shown in FIG. 3d. it is also considered that a negative charge equiva lent to or more than the aforementioned remaining positive charge in amount is injected into and stored in the base 2 or the boundary layer between the photosensitive layer l and the base 2 from the electrode 13' (FIG. 3C and Next, when the photosensitive member containing the electrostatic latent image formed as described above is brought close to a liquid, the interfacial tension between the surface of the said photosensitive member and the said liquid is affected depending on the presence of or on the intensity of electrostatic charge, and the said surface is wetted by the said liquid selectively or in different degrees depending on the aforementioned electrostatic pattern. Therefore, the said light portion where a high electric field is formed is wetted, and the said dark portion is not wetted (FIG. 3e). If the liquid used in this case is colored, a visible image can be obtained.

When a colorless transparent hydrophobic liquid is used to wet the photosensitive member, the said light portion is wetted and, if the resistance of the transparent liquid used is reduced here, the electrostatic latent image is destroyed. Next, when developed with a colored hydrophilic liquid, only the said dark portion on the surface of the photosensitive member, the said light portion of which has already been wetted by transparent hydrophobic liquid, is wetted by the colored liquid due to the repellent power of the hydrophobic liquid. As a result, a visible image is formed since only the dark region of the photosensitive member is wetted by the colored liquid (FIG. 3f).

It is considered desirable that the composite dark resistance of the photosensitive layer used in this invention is less than l0 lO' Q -cm. It is also considered desirable that the resistance of the base according to this invention is more than 9 -cm. It is desirable to form a barrier layer having a resistance of over lO fl -cm between photosensitive layer and base when a conductive base is used. The higher the resistance of the base and barrier layer, the more the applied voltage is required to be increased. This is explained by the presumption that the voltage is proportional to the relative ease of the initiation of injection or ejection of electric charge from the electrodes. However, it is considered that the base or barrier layer should have a resistance sufficient to hold and form the electric charge. Further detail will be understood by referring to the examples 1] and 12 described later.

As for the developing roller or the developer supplying means used in the developing process of the aforementioned image forming process, a highly excellent visible image can be obtained by using a developer supplying means of No. I through No. 3 type explained as follows. Detailed explanation of them will be provided later.

Next, an image forming process using another embodiment of this invention will be described. The feature of this process is to visualize the latent image by projecting an optical image on the photosensitive member used in the aforementioned image forming process, by applying the developer while providing an electric field across the photosensitive member either simultaneously with or after the projection, and by letting the photosensitive member attract the developer either selectively or in different degrees in inverse proportion to the amount of electric charge ejected from the electric field. The difference between this process and the firstly mentioned image forming process is that application of electric field and developer is not made separately but simultaneously, and the image forming process is essentially different from the first image forming process.

When a photosensitive member comprising a photoconductive layer having a small composite resistance and a conductivity that changes with the intensity of light and a base having a resistance nearly equal to that of insulation is exposed to a pattern of light or other radiation and an electric field is made to scan over the photosensitive member either simultaneously with or after the exposure, and a liquid is supplied to the neighborhood of the said photosensitive member, the liquid is attracted to the region where the conductivity of the photosensitive member has a low conductivity because the ejection of electric charge to the electrode is difficult and wetting action is produced, whereas in the region where the conductivity is increased by radiation, ejection of electric charge to the electrode occurs intensely and the wetting action of the developer is disturbed because the developer is repelled by the dynamic shift of electric charge at time of the said charge ejection. As a result, the interfacial tension between the said liquid and the surface of the said photosensitive member is affected by the presence or absence of the aforementioned electric charge ejection or by the degree of ejection, and the surface of the said photosensitive member is wetted by the said liquid according to the ejection pattern of the said electric charge. Therefore, in contrast to from the aforementioned first image forming process, the developer sticks not by the presence of electrostatic charge, but the ejection of latent image charge and injection of charges of different polarity is caused in the latent image region at time by applying electric field, and the developer is attached selectively by the repulsion of developer due to the transient phenomenon.

Explained more concretely by referring to FIG. 5, and FIG. 6, taking a photosensitive member comprising a photosensitive layer 11 of ZnO bonding agent having a small resistance compared with conventional photosensitive layers and a base 12 having a resistance near insulation, the mobility of electron of ZnO is greater than positive holes and ZnO is a majority carrier since ZnO is a N-type photosemiconductor. Therefore, as shown in FIG. 5a, thermally excited from electron F and electron caught at the trap level are considered to be present in the photosensitive layer even in the dark. When an exposure of a light and dark pattern is given to the surface of the aforementioned photosensitive member in the dark, a great amount of free carrier F (positive hole, electron) is considered to be produced in the neighborhood of the surface of the photosensitive member of light portion L (FIG. 5b). Next, when, for example, a DC voltage is applied across the electrodes after placing closely a electrode 13 covered with liquid (1) on the photosensitive layer side of the photosensitive member and a electrode 13' on the base side, respectively, a large amount of negative charge is considered to be ejected from the light portion L and the remaining negative charge is considered to be ejected from the dark portion D of the photosensitive layer to the electrode (FIG. 5c), and positive charge equivalent to the ejected charge in amount is considered to remain in the photosensitive layer as shown in FIG. d. On the other hand, it is considered that a negative charge equivalent to or more than the amount of the aforementioned remaining positive charge is considered to be injected from the electrode into and stored in the base 12 or the boundary layer between the photosensitive layer 11 and the base 12 (FIG. 50). When the aforementioned negative charge is ejected toward the electrode, the interfacial tension between the surface of the photosensitive member 11 and the liquid 1 is affected by the amount of electric charge ejected from the photosensitive member and the wetting action is produced in inverse proportion to the degree ofcharge ejection, and the liquid is attracted to wet at the dark portion D, whereas the liquid is repelled at the light portion L and no wetting action is produced. Consequently, a visible image is formed by the change in surface tension of the liquid due to the ejection of electric charge (FIG. 5d).

The aforementioned image forming process is different from the process in which development is carried out by applying in situ to the electrical latent image formed on the photosensitive member an electric field employing electrodes during development to extract the electrical latent image formed on the photosensitive member in, that an electric charge different in polarity to the said latent image is injected while the developer is applied. and that the developer is attached dynamically during mobile period of the electric charge. As a result, the developer adheres to the portion where no electric latent image is present. Especially, when the developer is applied, injection and ejection of the charge ofelectric latent image is started by the influence of electric field. However. as shown in FIG. 1d, the electric charge injected from the base 2 side is held in the interface between the base 2 and the photoconductive layer 1 due to the high resistance of the base, and due also to the high resistance. the charge of latent image formed on the photoconductive layer is retained without recombining with the charge on the base side to cause fade. As a result, the photoconductive layer. regardless of the low resistance, has an excellent latent image holding capacity and a latent image having an extremely good contrast is formed. Moreover. since nonpolymer material capable of controlling the lyophobic and lyophilic properties arbitrarily is used as the bonding material of the photosensitive member used in the above. if the surface of the photosensitive member is made Iyophilic in advance. the region where the charge ejection is constrained has more accelerated wetting action due to the lyophilic property of the bonding agent. and a visible image higher in density than the conventional images can be obtained. This is one of the features of this invention.

When the polarity of the electrode roller is changed, the visible image formed on the photosensitive paper is reversed. However, for the photosensitive paper using a N type photoconductive substance, it is preferrable to make the photosensitive layer side as electrode and the base side as electrode. In the photosensitive paper using a P type photoconductive substance or other organic photoconductive substance the electrodes are not limited to the above arrangement.

Furthermore, it is desirable to select a proper applied voltage depending on the kind of photosensitive member. It is possible to use nearly insulating materials as the material for electrodes. In this case a voltage suffi cient to pass the electric charge through the insulating body by producing tunnel effect is desired.

In the aforementioned image forming process. wetting development was carried out by using a photosensitive member comprising a low resistance photoconductive layer using nonpolymer bonding material and a high resistance base and by the dynamic mobilization of the latent image charge. Therefore. what is most different from the aforementioned first image forming process is that the application of electric field and developer is performed simultaneously and that the devel oper is repelled by dynamic transient characteristic of latent image charge, that is. by the injection and ejection of electrical charge. Therefore, since the developer is added at the same time as the final latent image is formed. no attenuation occurs in the latent image and an extremely good quality visible image can be obtained. Further detail will be clearly understood by referring to the example 13 described later.

The first type of developer supplying means used in this invention comprises projections having pointed ends provided on a smooth surface at proper intervals. This will now be explained on a concrete embodiment referring to FIG. 7 through FIG. 10.

FIG. 7 is a partial cross section of developer suppying means. F is a smooth surface body of the developer supplying means and is made of corrosion proof materials used in general printing concerns such as zinc. aluminum, paper, ether metals, and plastics. The surface fof the body F is desired to be made of lyophilic materials or made lyophilic by surface treatment or processing when a water soluble ink is used as the developer. Projections P are formed on the surfacefof the smooth surface body F. As the material for projections R. the photoresist, which is in wide use in printing techniques. is especially effective. It is especially desirable to use a metal that has undergone lyophobic treatment or processing for the projection P to have its surface lyophobic when a water soluble developer is used. It is desirable for the shape of the projection P to have an acute angle pointed end. The desirable diameter of the end is between several p. and several tens of p and the desirable height of the projection is within the range of 5 to I00 11., although it varies with the kind of photosensitive material.

The spacing between two adjacent projections differ similarly with the kind of photosensitive material and, when the photosensitive material is composed of less flexible bases such as metals, the bending of the surface of the said material is also small. Therefore, the interval between, for example. projections P and P which are perpendicular to the direction A in which the developing roller rotates is desired to be from 30 mm to l00mm.

However, when the base of the photosensitive material is composed of soft and easily-bent materials such as paper, the said interval is desired to be sufficiently small to keep the surface of the photosensitive member horizontal. For example. the interval between the projection P and the projection P is desired to be made to 10mm to 50mm. As for the projections arranged in the direction the developing roller rotates, the interval varies with the diameter of the roller, speed of the roller, and the photosensitive material. For example. the interval between the projection 11 and the projection 12 is desired to be 5mm to 30mm.

By constituting the liquid supplying surface as described above, the photosensitive body contacts only with the end of the projection P as shown in FIG. 2, and the supplying surface except for the projections is wet ted uniformly in film form by the developer.

As has been described so far, since the developer holding surface of the aforementioned developer supplying means is provided with many projections which are the same in height and have extremely sharp ends, the photosensitive member is held at a constant distance from the developer supplying means by those projections, and the developer address uniformly and indifferently to the photosensitive member. The developer sticks and wets the latent image forming region of the photosensitive member. However, the projections in contact with the photosensitive member are free from the adherence of the developer. Moreover, since these projections have very sharp ends as mentioned above, they have no special influence on the imageformation. As a result, the visible image obtained has an excellent resolution power.

FIG. shows a device constructed by using the developer supplying means shown in FIG. 7 through FIG. 9, in which 103 shows the photosensitive member comprising the base 102 and the photoconductive layer 101. The developer L in the developer tank V is supplied uniformly to the surface of the developer supplying roller R by the roller r. On the surface of the developer supplying roller R is affixed the aforementioned developer supplying means F, and the roller R is no tated on the electrostatic latent image holding surface of the photosensitive member, making contact with the projections P ofthe said means. On the base side of the photosensitive member is arranged the electrical-fieldapplying roller R, and the developer is applied to the photosensitive member while an electrical field is being applied to the photosensitive member by the rollers R and R'. Reference should be made to the aforementioned description of the image forming process of the second type for the developing process of this device.

The smooth surface fof the above-mentioned developer supplying means is not always required to be a smooth surface but is required to be a surface sufficient to hold and form the liquid uniformly. There can therefore be used such porous substances as sponge, fiber, and sintered metals. Moreover. there can be a fine regularly or irregularly uneven surface such as a metal surface that underwent sand setting.

In order to form the projections P. techniques such as etching process or electrodeposition process used the printing field can also be used.

Further detail will be clearly understood by referring to the examples l4 and described later.

FlGS. 11 through l4 show an embodiment of the second type of developer supplying means. Different from the above-mentioned system, this embodiment features the system by which the developer is supplied to the photoconductive layer intermittently by physical action, using a smooth surface that has both lyohilic property and lyophobic property.

More concretely the feature of this second embodi ment lies in the fact that, when, for example, the devel oper used in wetting development is water soluble, the developer adheres to the lyophilic surface selectively, in other words, the liquid is kept in a separated state on the surface and supplied to the photoconductive layer, and the liquid is separated by physical action on the smooth surface which has both lyophilic property and lyophobic property. Another feature of this embodiment lies in the fact that the division of developer is more easily performed on a smooth surface when on the smooth surface that has lyophilic and lyophobic properties the lyophobic portion is first wetted by lyophobic solution and then the lyophilic portion is wetted by using a water soluble developer. Specific embodiments will be explained in the following referring to FIGS. ll and 12, which show the cross section and the top view of the developer supplying means. H is prepared by forming grooves of l line/1mm order on a plate having lyophilic surface P, by filling a lyophobic substance into the said grooves, and by establishing finely divided lyophilic surface portions and lyophobic surface portions on the same surface alternatively. As the specific means of forming the above-mentioned embodiment the following method can be used as an example.

lv Lyophobic portion and lyophilic portion are divided into lines or mesh points within the range of l line/mm to 20 lines/mm by using the plain intaglic manufacturing technique of printing. Specifically, this is done as follows.

Prepare a smooth surface S having lyophilic portion P and lyophobic portion H as shown in FIG. 11 through the following process.

Preparation of plate application of photosensitive liquid printing (line, mesh positive (negative)) dyeing rinsing and development etching removal of residue correction -v fat sensitization of image stripping off of membrane etching solution treatment water rinse rubber application flat intagliov Either the negative or positive can be used as shown in FIG. 11 (a) (c) when the both portions P and H are further divided into lines or meshes shown in FIG. 12. It is sufficient to select the desired range of the ratio between the lyophilic portion and lyophobic portion depending on the degree of meshing. As the material for plate. zinc, aluminum, and PS plate now in general use are used. As the photosensitive liquid, the potassium dichromate colloid photosensitive liquid, diazophotosensitive liquid, etc. available on the market can be used.

FIG. 12 (a) (b) show the formation of lyophobie portion H and lyophilic portion P through the mesh point division using that plate process of printing. FIG. 12 (c) (d) show the fomation of lyophobic portion H and lyophilic portion P by line breaking-up and screen breaking-up with the same process. The degree of breaking-up and the shape can be made to the level of some 20 lines/mm by selecting a proper pattern at time of breaking-up printing, and the size of the point is allowed to be selected freely.

2. Fine holes or recesses within the range of 1 line/mm to 20 lines/mm are made of the base plate by using printing plate making techniques such as letterpress, intaglio press, photogravurepress, and fiat press. The concaves formed on the said base plate are filled with a material either lyophilic or lyophobic to form a smooth surface. The said surface comprises lyophilic portion and lyophobic portion.

For example, fine holes 50 a in diameter and 30 pt in depth were prepared lines/mm on a zinc sheet 300 p. in thickness using the method that prepares photogravure press. An epoxy resin was used to fill the said holes. The resin was applied uniformly over the zince sheet. dried. then the surface was polished with 150 mesh sandpaper until the surface of zinc was revealed uniformly. Thus a smooth surface S that had lyophilic portion P (zinc portion) and lyophobic portion (epoxy resin portion) was prepared.

3. Grooves (transversal grooves. longitudinal grooves. mesh form grooves) several p. to several mm in depth and distributed in the proportion of l line/mm to lines/mm are prepared. for example, on a metal roller by using mechanical processing technique. chemical etching processing technique, or electric surface treatment technique. The said grooves are filled with a lyophobic material such as an oil soluble resin to provide smoothpess on the surface of the said roller and to provide a lyophilic portion and lyophobic portion. As the material for the said roller. such materials as synthetic resins. synthetic rubbers. glass. and ceramics are used besides metals.

For example. grooves 50 a in depth and distributed in 2 lines/mm were engraved on the surface of a brass roller 30 mm in diameter and 2H) mm in length by using mechanical processing technique. The said grooves were filled with epoxy resin by forming a uniform film of the resin on the surface of the said roller. After drying. the surface of the said roller was polished until the brass surface was revealed uniformly. Thus smooth surface S that has lyophilic portion P (brass portion) and lyophobic portion H (resin portion) was made.

As the material for the screen. materials such as fibers can be used besides metals. For example. a film of epoxy resin was formed to fill a stainless steel screen of 300 mesh with the resin. After drying. the surface was polished until the stainless steel screen was uniformly revealed. Thus a smooth screen 5 having lyophilic portion P (stainless steel screen portion) and lyophobic section H (resin portion) as shown in FIG. 12 (a) was obtained.

FIG. 13 and FIG. 14 show an example of developing device using a developing roller made by making the above-mentioned developer supplying means into a roller. For the coating rollers R and R rollers made of materials having a porous surface such as sponge or rollers having many grooves are desirable.

In FIG. 13, the developer L in the tank V is spread on the developing roller R The photosensitive member 103 that comprises the base 101 and the photosen sitive layer 102 is charged by corona discharge in advance. and bears an electrostatic latent image that was formed by image projection undergoes wetting development by the developer L (Refer to FIG. I). Developer L is coated on the lyophilic portion P of the surface S of developing roller R when the said photosensitive member 103 passes through the space between the developing roller R and feed roller R and a good quality visible image that corresponds to the electro static image can be obtained.

It is possible to control the degree of wetting by applying a voltage E of several tens to several hundreds of volts across the developing roller R, and feed roller R and by determining the polarity. Next. in FIG. 14,

the tank V is filled with a solution 0 which is lyophobic to developer and the tank V is filled with a developer. Each liquid is coated on the developing roller R by coating rollers R and R respectively. and distributed separately to the lyophilic portion P and lyophobic portion H of the surface. The developer L is coated on the lyophilic portion P and the liquid 0 that is lyophobic to the developer is coated on the lyophobic portion P. Next. only the developer portion is transferred to the intermediate lyophilic blanket roller R When the photoconductive body 163 that carries an electrostatic latent image passes between the blanket roller R and the feed roller R wetting development is done by the developer on the blanket roller R and a good quality visible image can be obtained. In this case the blanket roller R can be removed. It is possible to control the degree of wetting by applying a voltage of several tens to several hyndreds of volts across the developing roller R. and the blanket roller R or across the blanket roller R and the feed roller R In FIG. l3 and FIG. 14, a good quality normal or reversal visible image can be obtained by applying a voltage of several hundred volts across the developing roller and the feed roller and by selecting the polarity when passing a photosensitive member that carries a conductive latent image which was formed corresponding to the image projection without previous application of electrostatic charge.

When applying a voltage across the feed roller and the developing roller. a metal roller. a semiconductive rubber roller. or a roller having the surface treated to be conductive or semiconductive is desirable as the feed roller R This limitation is not applied specifically when no voltage is applied.

FIGS. I6 through 21 show the third type ofdcveloper supplying means according to this invention. The features lie in the depressions 202 such as grooves in the proportion of l line/mm to 20 lines/mm or conical holes in the proportion of l/mm to 2(J/mm. that are capable of holding the developing solution by means of capillary phenomenon. which are prepared on the roller or plate of the developer supplying means. the bottoms of the depressions 202 are made ofa lyophilic materials and the surface of the projections 203 are made of a lyophobic material. With such a construction as described above, the developer 204 stays only on the depressions 202 and does not stick to the projections 203. Therefore, when arranged as shown in FIG. l5, only the projections 203 contact with the surface of the photosensitive paper. and an electric charge of opposite polarity to the electrostatic latent image is produced on the surface of the developer contained in the depression 202 that faces the latent image forming surface. and the surface tension of the developer 204 is reduced by the charge. As a result, the developer 204 spreads along the internal wall of the depression 202 and over the surface of the photosensitive paper to develop the latent image. On the other hand. since no electric charge is produced on the surface of the developer that faces the nonimage area, the surface tension of the developer 204 is not reduced. and the developer cannot reach the surface of the photosensitive paper. Consequently. since the developer 204 sticks only to the image section and does not stick to the nonimage section of the photosensitive paper 205, the latent image charge is prevented from dissipating. the image section is protected from staining, and a good quality image can be developed.

The examples of the developing roller and the devel oping plate according to this invention will be clearly understood by referring to the examples 16 through 21 described later.

The developer supplying means used in the abovementioned examples are all shaped in drums and so contracted that a hygroscopic supply roller, for example a rubber roller or a sponge roller, absorbs the developer in the developer tank and supply it to the drumshaped developer supplying means.

However, in the case in which a supply roller having a smooth surface is used, a large amount of developer is supplied to the surface of both ends of the developer supplying means and the amount of developer supplied is decreased as the distance between the surface and the middle point of the roller is reduced and, as a result, the density ofthe image obtained on the photosensitive member is lowered the closer the image is to the central portion. This is a drawback of this type of developer supplying meansv lt has been found that a roller construction, that supplies the developing solution on the entire surface of developer supplying means uniformly and continu ously without having the abovementioned defect, can be obtained very easily by forming grooves to be filled with liquid on the suface of the supply roller by winding a fine metal wire or synthetic resin thread around the surface of the supply roller.

FIGS. 22 and 23 show an example of a developing device that employes such a supply roller. In FIG. 22, 303 is an electrophotographic photosensitive member comprising a base 302 and a photoconductive layer 301 formed on the base 302. R is developing roller and R' is a feed and pressure roller for the photosensitive member 303, r is a developer supply roller which supplied the developer in the container V to the developing roller R. The developing roller R can be a metal roller having a smooth surface. but an extremely good image can be obtained by using the abovementioned first to third types of developer supplying meansv S is a bias power source that applies a voltage across the rollers R and R. P is a pressure spring that acts on the roller R and is so constructed that it presses the roller R only when feeding the photosensitive member 303 and pulls up the roller R when the photosensitive member 303 is not between the rollers R and R to prevent the rollers R and R from contacting with each other and the bias power source S from being shortcircuitted.

The developer supply roller r has the grooves 305 on its surface as shown in FIG. 23 which are formed by winding a fine wire 304 for example a fine metal wire or synthetic fiber bundle, around its surface.

In FIG. 22 when the supply roller r starts rotation, the developer L in the developer container V is filled in the grooves 305 on the supply roller r uniformly. As a result, the developer sticks uniformly to the surfaces of the supply roller r. Since the supply roller r rotates while contacting the surface of the developing roller R, the developer L on the supply roller r sticks to the entire surface of the developing roller R uniformly. Therefore, the developer L is given to the developing roller continuously and uniformly by the continuous rotation of the supply roller. Since an electrostatic latent image has been formed on the photoconductive layer 301 of the photosensitive member 303, when the developer is supplied to the photosensitive member by the developing roller R and when, at the same time, an electric field is given to the photosensitive layer by the bias power source S connected to the rollers R and R', a visible image is formed according to the abovementioned second type of image forming process.

Although the rotating direction angle 9 which is formed by the contact position of the supply roller r and the developing roller R and the contact position of the developing roller R and the paper feed roller R must be changed depending on the viscosity of the developer and the diameters of the rollers, it was experimentally confirmed that the angle lower than was desirable.

The specific construction of the abovementioned supply roller will be better understood by referring to the examples 22 through 25 described later.

In each of the developing process that has been described so far, the developer is supplied to the photosensitive member by developer supplying means such as the developing roller and the said developer is wet applied to the electric latent image of the photosensitive member and the action of the said latent image. However, the wetting development by means of developer supplying means such as the roller does not result in a sharp image of good resolution power unless the rollers of special constitution such as used in the first through the third types are used. This invention includes the novel developing method as mentioned, in which a photosensitive member capable of controlling the ratio between the lyophilic portion and the lyophobie portion and the surface of the said photosensitive member uses a nonpolymer bonding agent which is uniformly constant with respect to the lyophilic and lyophobic propertiesv The feature of this developing method is that; an electrostatic image is formed on a photosensitive member, the surface which has been made sufficiently lyophobic by the addition of a nonpolymer bonding material, for example a higher fatty acid. The developer is poured onto the said surface; the interfacial tension that acts upon the surface of the developer and the surface of the photosensitive member is changed by the effect of the electrostatic latent image. The electrostatic latent image causes a change in the shape and size, of the contact angle of the developer body that flows down on the photosensitive memher. As a result, only the region where the latent image,

is present is wetted and the region where the latent image is absent is not wetted at all by the lyophobic,

property of the surface of the photosensitive member, and resultant development is performed.

It is a well known fact that, in general, when a water drop rotates on a lyophobic surface, the water drop cascades on the lyophobic surface taking all shapes of sphere, ellipsoid, and island. This is a physical phenomenon caused by the change in the interfacial tension between the surface and the water drop, or the contact angle, due to the presence of nonuniformity in the lyophobic property of the surface. The abovementioned developing method according to this invention applies such physical phenomenon to the developing method. Development is performed by cascading a developing solution made by adding coloring agent to a watery solvent such as water along a lyophobic surface. In this method the phenomenon that the lyophobic surface is turned into lyophilic when, especially, an electrostatic image is present on the said surface and, is used to make the falling developer wet and stick only to the latent image region.

Such a developing method will be explained referring to FIG. 24, in which 401 shows a photosensitive member that has a photoconductive layer on the base. The photosensitive member 401 has a photoconductive layer made of zinc oxide and as the bonding material. nonpolymer material and a higher fatty acid (Refer to the examples 26 through 32 for the specific composition of the photosensitive member). The photosensitive member 401 is placed on a metal holder 402. The metal holder 402 is placed tilted with an angle of slope of 60. An electrostatic latent image has already been formed on the photosensitive member 401. On the other hand. a developer tank 403 is placed above the photosensitive member 401 and the said tank contains a developer for wetting development made by adding a coloring agent to water or t9 a watery solvent.

During development, the developer in the developer tank 403 falls on the photosensitive member and the developer rotates on the photosensitive member in cascade because the photosensitive member is placed inclined. The developer flows into the developer pan 406. During the period of the rotation of the developer on the photosensitive member the developer wets and sticks to the latent image region of the photosensitive member. but the developer does not stick to the nonlatent-image region because the photosensitive member has a lyophobic surface there. The developer continues falling. The abovementioned developing method is extremely effective in practice because the said method does not need developing means such as the developer supply roller and allows a good quality image to be obtained. Refer to the examples 26 through 32 described later for specific composition.

EXAMPLE 1 C'hlorazol black E Pure water gr 400 ml A uniform 150 V negative charge was given to the suface of a photosensitive member 3 comprising a photoconductive layer 1 and a base 2 by negative corona discharge initially. Next an exposure for about 2 seconds was given by a 30 W tungsten lamp (at a distance of 30 cm) by way of a positive original pattern. The image was developed and made visible by the device that had two rollers R and R as shown in FIG. 1. The roller R of this device was an aluminum roller 30 mm in diameter and 210 mm in length. The roller R was 30 mm in diameter and 2lO mm in length. The surface of the roller R was made of sheet zinc on which a photoresist dot pattern l50 lines/inch in density was prepared by planography print technique. The developer L was supplied to the hydrophilic surface of the roller R uniformly from the developer container by using the developer supply roller r. The roller r was a porous sponge roller 20 mm in diameter and 210 mm in length. Thus a black positive visible image, that corresponded to the electrostatic charge pattern and was excellent in hlaf tone, was obtained.

EXAMPLE 2 I00 ml 50ml Water India ink (Taguchi Col An exposure of about 400 Lux-sec was given using a 60 W tungsten lamp (at a distance of 50 cm) by way of a positive original pattern. A good quality positive visible image was obtained after development that is similar to the Example I. The developing roller R was an alumi num roller. 30 mm in diameter and 210 mm in length. having a surface almite plated.

EXAMPLE 3 A photosensitive member was obtained by dissolving 4 gr ofzinc naphthenade completely into 30 ml of toluene and by dispersing 10 gr ofZnO in the same manner as the Example I. A 2-minute of image projection with a 60 W tungsten lamp and a distance of 30 cm was given to the photosensitive member in advance by way of an positive original pattern, and then development was performed in the same manner as the Example 2. In this case a voltage of 500 V was applied across the developing roller R and paper feed roller R from the DC power source, having the polarity on the roller R and polarity on the roller R. The roller speed was 10 cm/sec. A good quality positive visible image that corresponded to the conductive latent image was obtained.

EXAMPLE 4 A photosensitive member was prepared by applying a uniform 8 p. thick coat of an emulsion, obtained by first dissolving 2 gr. of abietic acid in 30 ml of ethylalcohol and by dispersing 10 gr of ZnO and 0.l gr of tributyl phosphate for about 7 minutes with ultrasonic waves, to the surface of the art treated paper about [.t in thickness (RH: 50%, resistance: l0 l 0".0. -cm), and by natural drying the paper for 3 days in the dark. First, an electroconductive latent image was formed by exposing image-wise for I second in the dark place from a I00 W tungsten lamp (30 cm in distance) by way of a positive original pattern, then the said latent image was converted into an electrostatic charge latent image by a device as shown in FIG. 2, which is provided with conductive rollers C and C. The photosensitive side I was made to have the polarity and the base side was made to have the polarity. then a voltage of 500 V was applied from the DC power source 6 across the roller electrodes and the photoconductive member was made to close contact with the rollers and be charged. An electrostatice latent image was formed 

1. AN IMAGE FORMING PROCESS COMPRISING THE STEPS OF, FORM, ING AN ELECTRIC LATENT IMAGE ON THE PHOTOCONDUCTIVE LAYER, DEVELOPING THE THUS OBTAINED ELECTRIC IMAGE BY ADDING A DEVELOPER LIQUID COMPRISING AN AQUEOUS SOLVENT CONTAINING COLORING MATTER SO AS TO CONTACT THE DEVELOPMENT TO THE SAID LATENT IMAGE REGION, THE AFOREMENTIONED PHOTOCONDUCTIVE LAYER HAVING A PRACTICALLY LYOPHOBIC SURFACE AND CONTAINING PHOTO CONDUCTIVE SUBSTANCES AND NON-POLYMERS AS THE BONDING MATERIALS WHEREIN THE NON-POLYMER BINDING MATERIALS ARE SELECTED FROM THE GROUP CONSISTING OF ORGANIC ACIDS, ORGANIC ACID ANHYDRIDES, PHENOL DERIVATIVES, AMINO ACIDS, METALLIC SOAP, SUGAR AND DERIVATIVES THEROF, AND ALKALI METAL SALT OF ORGANIC ACIDS
 2. An image forming process according to claim 1, wherein the aforementioned photoconductive layer comprises a photoconductive substance, a binder selected from the group consisting of organic acids, organic acid anhydrides, phenol derivatives, amino acids and a compound selected from the group consisting of a higher fatty acid, higher fatty acid ester and higher alcohol.
 3. An image forming process according to claim 1, wherein the aforementioned photoconductive layer contains electron accepting/donating substance sensitizers.
 4. A process according to claim 1 wherein the photoconductive layer has sensitizing dyes.
 5. The image forming process of claim 1 including the steps of: preparing an electrophotographic photosensitive member containing a base and a photoconductive layer adapted to hold an electric latent image on said photoconductive layer; forming an electric latent image on said layer; passing said member bearing said latent image through an electric field; and thereafter, developing the thus obtained electric image, wherein said photoconductive layer has an effective dark resistance of less than 10.sup.13 ohms-cm.
 6. A process according to claim 5 wherein the aforementioned base comprises a substance having a specific resistance of above 10.sup.9 .OMEGA. -cm.
 7. A process according to claim 5 wherein a barrier layer having a barrier resistance of above 10.sup.9 .OMEGA. -cm is formed between the base and the photoconductive layer of the photosensitive member.
 8. A developing process comprising the steps of: preparing an electrophotographic photosensitive member that holds an electric latent image and has a photoconductive layer which has a practically lyophobic surface; and contacting a developer liquid comprising an aqueous solvent containing a coloring matter only to the latent image region of the photosensitive member by cascading the developer to the surface of the photosensitive member, the photosensitive member containing a photoconductive layer which contains photoconductive substances and non-polymer bonding materials selected from the group consisting of organic acids, organic acid anhydrides, phenol derivatives, amino acids, metallic soap, sugar and derivatives thereof, and alakli metal salts of organic acids and said photoconductive substances and non-polymers being arranged in weight ratios ranging from 1:1 to 8:1 said photoconductive layer having an effective dark resistance of less than 10.sup.13 ohm-cm.
 9. A process according to claim 8 wherein the photoconductive layer comprises a photoconductive substance, a binder selected from the group consisting of organic acids, organic acid anhydrides, phenol derivatives, amino acids, metallic soap, sugar and derivatives thereof, and alkali metal salts of organic acids and a compound selected from the group consisting of a higher fatty acid, higher fatty ester and higher alcohol. 